The misfortune known as Dennis Seidenberg’s injured right knee has also been considered an opportunity.

The window that opened Dec. 28, the first of 44 regular-season dates without their second-best defenseman, has allowed the Bruins to take a wide-angle look at their defense in context of another playoff run.

The Bruins are 5-5-1 without Seidenberg, allowing 2.82 goals per game. This season, they’ve given up 2.16 goals per game, second-fewest behind Los Angeles (2.04).

The Bruins improved in their last three games, in which they totaled five points against Dallas, Chicago, and Los Angeles. They allowed two goals in each game.

In those games, Zdeno Chara was Zdeno Chara — the No. 1 strongman tasked to shadow three top lines. Most of Chara’s help came from Johnny Boychuk, who could be his regular righthand man in the postseason instead of Seidenberg.

Matt Bartkowski, the team’s fastest and most agile puck-carrying defenseman, has played 20-plus minutes in three straight games. It is his longest stretch of the season above 20 minutes. Bartkowski’s high-end physical skills compensated for his average hockey sense and untimely penalties.

But the 11-game period reminded the Bruins that injuries will take place. Dougie Hamilton has been absent the last four games because of a concussion. Adam McQuaid (leg) is off the ice for a third time this season. Their durability is in question.

The Bruins went through similar circumstances last season when Seidenberg (hamstring) and Andrew Ference (foot) missed time in the playoffs. The Bruins have no intentions of being shorthanded on defense for a second straight postseason.

The trade deadline is March 5, but it is a deceiving date. The Bruins play their final game before the Olympic break Feb. 8. The deadline is one week after their first post-break game against Buffalo Feb. 26. The Bruins have approximately four weeks of NHL business in which to acquire their preferred player.

The hockey operations department, which held its pro scouting meetings in Las Vegas last week, wants a defenseman with an expiring contract. The Bruins must save money to re-sign Torey Krug and Reilly Smith. Given their offensive production, both players could triple their current annual salaries ($925,000 for Krug, $900,000 for Smith). Neither Krug nor Smith is eligible for arbitration.

Bartkowski and Niklas Svedberg, Chad Johnson’s projected replacement next season, will also be restricted, although the Bruins could put both in play on the trade market. Jarome Iginla and Shawn Thornton will be unrestricted.

The Bruins would prefer a left-shot defenseman, preferably a stay-at-homer. The Bruins have three left-shot defensemen in Chara, Bartkowski, and Krug. David Warsofsky, recalled twice this season, would be a fourth.

The Bruins have more right-side depth with Boychuk, Hamilton, McQuaid, Kevan Miller, and Zach Trotman. The coaching staff prefers the defensemen to play their strong sides.

The asking price for such players is usually a draft pick and/or a prospect. The Bruins have six picks in the upcoming draft. They traded their fourth-rounder to St. Louis for Wade Redden last season. Of their young players, Bartkowski, Svedberg, and Trotman would bring the most return.

Some trade targets:

Chris Phillips, Ottawa. The Bruins have a strong Ottawa connection, starting with general manager Peter Chiarelli, formerly the Senators’ assistant GM. Phillips, unrestricted after this season, would be reunited with Chara and Chris Kelly. Phillips would be an experienced, physical, and reliable second-pairing defenseman the Bruins could deploy against second lines. Landing Phillips would allow the Bruins to pair Chara with Boychuk. Ottawa doesn’t have a 2014 first-rounder, having used it to acquire Bobby Ryan from Anaheim. Two obstacles: Ottawa is still contending for a playoff spot, and Phillips has a no-trade clause.

Andrew MacDonald, Islanders. The 27-year-old is the best bargain in the league. MacDonald, who earns $550,000 annually, logs 25:57 of ice time per game, fifth-most in the NHL. MacDonald plays in all situations, including shutdown shifts against top forwards. MacDonald, unrestricted after this season, will be in line for a career score. If the Islanders think MacDonald will be too costly to re-sign and make him available, there will be a line resembling the Long Island Expressway at rush hour to acquire the left-shot defenseman. The Islanders have the third-worst record in the East, but they’re 7-3-0 in their last 10 games. They could make a late push.

Kyle Quincey, Detroit. The Red Wings, hammered by injuries all season, are in danger of missing the playoffs. If the Wings fall even more as the deadline approaches, they might be in the unfamiliar position of becoming sellers. The 28-year-old Quincey isn’t as physical as Phillips. Quincey relies on his skating to move the puck.

Henrik Tallinder, Buffalo. The 35-year-old relies on smarts and positioning to fend off attackers. Tallinder’s experience was the main reason Sweden picked the veteran for the Olympics over youngsters such as Victor Hedman and Jonas Brodin. Tallinder would be a respected and welcome presence in the room and on the ice. New Buffalo GM Tim Murray is eager to acquire assets.